Looking westward from the Apollo 16 CM toward the Descartes landing
site southwest of Tranquility Base. To find the site, look straight along
the gamma ray spectrometer boom one additional boomlength to the area between
two small bright craters. The distance on the surface is 71 km. This part
of the Moon's near side, the central highlands, is essentially devoid of
maria. Two major goals of this mission were to study the smooth plains
immediately west of (above) the site and the peculiar furrowed and hummocky
terrain that dominates the center of the frame. Before the mission, both
units were thought to have been formed by volcanism, but now, after analysis
of the samples, they are interpreted as ejecta deposits resulting from
very large impact events. The plains and furrowed materials have partly
covered and masked older craters in this region, including Descartes (D)
at the left of the picture, so that fewer craters are visible here than
in most farside and many near-side highland areas. The more mountainous
terrain along the bottom (east) is part of the Nectaris basin rim. (Dashed
lines are used to show the rim crest of crater Descartes, the rim of which
has been so severely degraded by erosional and depositional processes that
it is otherwise difficult to see. This convention is used frequently throughout
this volume. -D.E.W.